The present invention relates to an information recording apparatus provided with a magnetic conversion head and a magnetic recording medium, more particularly to a magnetic recording disk apparatus that has improved its track density.
Generally, in order to make a head follow up an object data track on a magnetic recording disk medium, the magnetic recording disk apparatus must enable relative positional information between the head and the magnetic recording disk medium to be kept measured accurately and a positional deviation caused by a thermal expansion difference between both magnetic recording disk medium and the arm that supports the head, as well as an influence of such a disturbance as rotation vibration of the spindle motor and the rotary actuator to be reduced. This is why special patterns for positioning the head are recorded on the magnetic recording disk medium before the shipping. The area in which such a pattern is recorded as shown in FIG. 6 is referred to as a servo area 31. The servo area 31 is formed between data areas 33 via a gap area 32. After the shipping, it is inhibited that the user records data in this servo area 31. In the servo area 31 is recorded data continuously between adjacent tracks 16 in the radial direction. The servo track width 311 is equal to the track pitch of the tracks 16. On the other hand, in a data area 33, recorded data on each track 16 is separated from another. The recording track width 331 is narrower than the track pitch of the tracks 16. Actually, 60 to 100 servo areas 31 are formed at equal pitches on a round of track 16 of the magnetic recording disk medium.
FIG. 7 shows a configuration of such a servo area 31. An ISG part 40 is a continuous pattern provided so as to reduce the influence of the distribution of the magnetic property in the recording film and the distribution of the flying height of the magnetic recording disk medium. The servo decoder circuit reads back the ISG part 40 by turning on the auto gain control (AGC). Upon detecting an AM part 41, the AGC is turned off, thereby the magnetic recording disk apparatus of the present invention normalizes the read-back amplitude of the subsequent burst parts 43 with the amplitude of the ISG part 40. A gray code part 42 describes the track number information of each track 16 with a gray code. This part 42 often describes sector number information, as well. The burst part 43 makes a houndstooth check pattern for obtaining accurate positional information in the radial direction. This part 43 is indispensable for following up the center of each track 16 accurately. This pattern 43 consists of a pair of A-burst 43-1 and B-burst 43-2 that are provided as straddle the center of each track 16 alternately, as well as C-burst 43-3 and D-burst 43-4 that are provided as straddle the edge of each track 16 alternately. A pad part 44 is a pattern provided so as to absorb the delay of the decoder circuit system to keep generating a clock while the servo decoder circuit reads back the servo area 31.
The head 11 reads back the servo areas 31 while running on the position C shown with an arrow from left to right in FIG. 7. FIG. 8(A) shows an example of the read-back waveform at that time. To simplify the description, the read-back waveforms of the AM part 41, the gray code part 42, and the pad part 44 are omitted here. The servo decoder circuit 44 detects the amplitudes of the four burst parts (from the A-burst part 43-1 to the D-burst part 43-4). The amplitude value of each burst part is converted to a digital value in the AD converter, then entered to a CPU. The CPU then calculates the difference between the amplitudes of the A-burst part 43-1 and the B-burst part 43-2, thereby finding the N position signal. Although an equation for normalizing the difference with the amplitude of the ASG part 40 is described in FIG. 7, this function is realized by hardware in which the servo decoder circuit locks the AGC so as to fix the amplitude of the ISG part 40. In the same way, the CPU obtains the Q position signal from the difference between the amplitude values of the C-burst part 43-3 and the D-burst part 43-4. FIG. 8B shows the position signals of the head, which are generated as described above. The N position signal becomes 0 at a position where the center of the head 11 straddles the A-burst part 43-1 and the B-burst part 43-2 equally. The N position signal becomes positive or negative almost in proportion to a deviation from this center position. For example, the N position signal at the position C shown in FIG. 8B can be obtained from the read-back waveform shown in FIG. 8(A) at the position C shown in FIG. 7. Usually, it is assumed that the edges of both A-burst part 43-1 and B-burst part 43-2 match with the center of each track 16.
The CPU inverts the status (positive/negative) of the N or Q position signal, whichever is smaller in absolute value, then links the signals, thereby generating a continuous position signal. This position signal is then compared with a target position, thereby finding an optimal current value to be applied to a voice coil motor 14 so as to perform such predetermined operations as following-up and seeking.
A technique for forming a spiral data track itself is disclosed in Japanese Published Unexamined Patent Application No. 62-204476, No. 63-112874, and No. 61-296531 respectively. A technique for forming spiral servo information itself is disclosed in FIG. 1 of Japanese Published Unexamined Patent Application No. 62-204476.
The above conventional techniques, however, have been confronted with a problem that non-uniformity of the direction of magnetization in the read-back element degrades the linear accuracy of the position signal, thereby the radial position of the head cannot be controlled accurately. In addition, those conventional techniques have also been confronted with a problem that because the detection accuracy of the position signal is degraded by a property variation of the read-back element, the radial position of the head cannot be controlled accurately.
In the recent years, however, it is common that a high read sensitivity head is used to increase the recording density of the object magnetic recording disk apparatus. For example, there are well-known techniques for using a read-back head that employs a magnetoresistive element (MR element) that makes good use of the magnetoresistive effect of the magnetic film itself, a giant magnetoresistive element (GMR element) that has improved the magnetoresistive effect with a non-magnetic film sandwiched by magnetic films, or a tunnel magnetoresistive element (TMR element) that has improved the magnetoresistive effect more with use of a phenomenon that a tunnel current is changed by an external magnetic field significantly. Those techniques are all effective, since each of those magnetoresistive elements can obtain a favorable SN ratio even in reading back fine recorded patterns on magnetic recording disks, thereby the bit density of the object magnetic recording disk apparatus can be improved.
Generally, both ends of a magnetoresistive element are structured so as to enable a bias magnetic field (vertical bias magnetic field) to be applied in the width direction of the track, thereby forming the magnetic film of the element in a single magnetic domain structure. Consequently, the read-back sensitivity is degraded with respect to the strength of the leakage magnetic field of the object disk at both ends of the element, thereby the output is not made in uniform in the width direction of the track. In addition, because the magnetizing direction is disturbed at both ends of the element, the amplitude value may differ significantly between positive side and negative side of the read-back waveform. And furthermore, the non-uniformity of the magnetizing direction, which is a problem mentioned here, may be varied in various forms due to the recording magnetic field generated by the write element provided adjacently to the magnetoresistive element. This phenomenon is referred to as a property variation of the read-back element. This property variation of the read-back element may also occur due to a change of the flying attitude of the head caused by a wear, a flaw, and a contaminant thereon.
Because the read-back sensitivity is low at both ends of the element, the read-back amplitude of the burst part 43 is not proportional to the radial position of the head. Both of N and Q position signals also do not become proportional to the radial position of the head exactly. If any asymmetrical component of the vertical amplitude is contained in the read-back waveform of the burst part 43, then the constant of the decoder circuit comes to depend on the position signal significantly, thereby the errors of both N and Q position signals become more serious. Because of those negative factors, the N and Q position signals of the magnetic recording disk apparatus that uses a magnetoresistive element do not become linear as shown in FIG. 8B. There is a technique for improving the accuracy for detecting the error level referred to as a non-linearity error of this position signal by creating a correction table and using the table. In this case, however, a correction table must be prepared for each head mounted in the magnetic recording disk apparatus and the table must be recorded in the memory of the package board 17 or in part of the management area on the disk 12 before shipping. Consequently, the management of production processes becomes complicated, and furthermore, the difference among properties of decoder circuits cannot be corrected even with this technique. Those factors have thus been an obstacle for the improvement of the track density of the apparatus.
Furthermore, the center of a track to follow up may be offset due to a change of the non-linearity error level if a property variation occurs in the read-back element. To avoid such a read-back error to occur due to a change of the property variation of the read-back element, therefore, a current is applied to the write element so as to execute a dummy write operation that applies an external magnetic field to the read-back element intentionally, thereby eliminating the property variation. This is a well-known technique. And yet, there is still another problem that must be solved. The problem is a fact that the content of the variation in a magnetized state differs between property variation of the read-back element related to the non-linearity of the position signal and the property variation of the read-back element related to a read-back error. The technique that performs a dummy write operation after a read-back error occurs cannot avoid a possibility that an offset from a target track, thereby overwriting is done on an adjacent track. This has been a factor for degrading the reliability of the magnetic recording disk apparatus.
This is why there has been expected appearance of a new technique that enables the non-linearity error of the position signal caused by the read-back property of the head and the servo decoder circuit property to be corrected so as to improve the positioning accuracy, thereby detecting the property variation of the read-back element related to the non-linearity error of the position signal and improve the data track density of the magnetic recording disk apparatus that employs a magnetoresistive element as the read-back element. It is thus possible to prevent the fatal error that overwrites data on adjacent tracks so as to improve the reliability of the apparatus.
In order to achieve the above objects, the magnetic recording disk apparatus of the present invention comprises a magnetic recording disk medium provided with a plurality of tracks formed thereon in a concentric circle pattern and a servo area formed on a part of each tracks and used to record a servo pattern; a magnetic recording head provided with a read-back element and a write element; and a servo decoder circuit for generating a head position signal from the servo pattern formed on the magnetic recording disk medium; wherein a plurality of patterns are disposed in an area different from the servo area on the disk medium. Each of a plurality of the patterns is deviated from another in the radial direction of the track at least by a width narrower than the width of the read-back element of the head.
Furthermore, a plurality of full tracks are disposed in some radial areas on the disk so that each of the full tracks is deviated slightly from another in the radial direction of the disk and the amplitude of the read-back waveform of each of those full tracks is detected while following up the track, thereby measuring the profile of each full track from the amplitude of the read-back waveform.
Furthermore, in the magnetic recording disk apparatus of the present invention, a plurality of micro-tracks are disposed in some radial areas on the disk so that each of those micro-tracks is deviated slightly from another in the radial direction of the disk and the amplitude of the read-back waveform of each of a plurality of the micro-tracks is detected while the track is followed up, thereby measuring the profile of the micro-track from the amplitude of the read-back waveform.
The magnetic recording disk apparatus is provided with a function for calculating an effective write or read-back width of the head from the profile of the full-track or the micro-track. The magnetic recording disk apparatus is also provided with a function for correcting the non-linearity of the head position signal from the profile of the full-track or the micro-track. The magnetic recording disk apparatus is further provided with a function for detecting a variation of the head position signal from the profile of the full-track or the micro-track. The magnetic recording disk apparatus is further provided with a function for detecting a variation of the head read-back property from the profile of the micro-track. In addition, the magnetic recording disk apparatus is further provided with a function for correcting the variation if the variation is out of a preset range.